The construction of pipelines generally involves the axial connection of two pieces of pipe to form a single pipeline conduit for transporting materials from one point to another. Along the pipeline there may be one or more fittings, which allow the pipe pieces to be joined to other components in the pipeline. The liquid or gaseous materials usually conveyed via pipelines require that the pipeline conduits and joints between axially-joined pieces of pipe, and between pipes and fittings, be substantially leak-proof. In addition it is advantageous for the axial joint to have significant strength so as to axially restrain the adjoining pieces of pipe as flow in the pipeline creates thrust forces between the pieces of pipe that tend to counteract the attachment forces axially securing the pipe joint. Those having skill in the art of pipeline construction are thus in search of pipeline components and securing methods for more completely securing pipeline joints to better meet the needs listed above as well as accomplish other objectives as listed in this application.
Existing methods for providing a secure pipeline joint can be distinguished from one another by the procedures and components utilized to form the pipeline joint. In addition, existing pipeline joints vary by the way the pipeline connection components, such as gaskets, locking rings, and other components, are placed and secured within the pipeline joint. The design parameters of a pipeline joint are affected by the methods and components used to construct a given joint, the types of materials transported by the pipeline, the environment in which the pipeline is situated, and other pipeline design factors.
One common method for connecting pipe together involves the insertion of an end of a male piping member (spigot) into an expanded end of a second pipe, the interior profile of which has been specially fabricated to form a socket (“bell socket”). The bell socket is sized to accommodate the spigot end of the male piping member to be received. This connection type is known in the pipe industry as a “push-on joint.”
In order to seal and secure a push-on joint, several methods are known in the art. One method involves inserting a fitted gasket within an annular recess formed within the bell socket. Such a gasket is often specially designed to both seal the pipe joint and axially-restrain the pipe spigot within the bell socket by employing stainless steel locking segments that are embedded circumferentially into the elastomeric material gasket as shown in U.S. Pat. Nos. 5,295,697 and 5,464,228 issued to J. Weber and L. Jones on Mar. 22, 1994 and Nov. 7, 1995 respectively. The locking segments in these gaskets extend from the interior surface of the gasket, and away from the interior surface of the bell socket, such that they grip the outer surface of the spigot when the pipeline conduit is subjected to internal pressures. These gaskets couple the axial restraint function with the sealing function in a single-gasket design.
Another method of axially joining pieces of pipe to form a pipeline conduit is referred to as a mechanical joint. In this method, the bell socket has an arrangement for axial attachment to a corresponding gland that is configured to slidably fit on the outer surface of the spigot. In mechanical joints such as those disclosed in U.S. Pat. No. 5,803,513 to Richardson, issued Sep. 8, 1998, an elastomeric gasket and a separate locking ring are positioned between the gland and the bell socket, so that as the gland is attached to the bell socket, the elastomeric gasket is compressed into a sealing position within the bell socket, and the locking ring is urged into contact with the outer surface of the pipe spigot. In the Richardson '513 Patent, the locking ring is prevented from prematurely engaging the spigot by the use of skid pads, which are added to the inner, toothed surface of the locking ring. While the skid pads in the Richardson '513 Patent prevent premature engagement of the locking ring with the outer surface of the spigot, they add cost of materials and labor to the construction of the underlying gasket.
Other mechanical joint pipe joints are disclosed in U.S. Pat. No. 5,398,980 to Hunter et al., U.S. Pat. No. 5,335,946 to Dent et al., and U.S. Pat. No. 4,878,698 to Gilchrist et al. In these patents, there are disclosed various mechanical joint methods utilizing a separate restraining (toothed split ring) and sealing (elastomeric gasket) element positioned within the bell socket and held in place by an axially-attached gland to seal and restrain pipe spigots in mechanical pipe joints. The Hunter '980, Dent '946, and Gilchrist '698 Patents all disclose the placement of the locking elements within the bell socket. As a result, less space is available within the bell socket for the elastomeric gasket. In addition, these methods require the use of two separate components (the split ring and elastomeric gasket) to restrain and seal the spigot within the mechanical joint.
EP 0334380 to Imhof et al discloses another mechanical pipe joint where the joint is sealed and locked by the interaction of several separate layered components including: (1) a clamping ring composed of a plurality of clamping segments, which are interconnected in the circumferential direction by a rubber layer, (2) a joint gasket made of soft elastomeric material, and (3) a sliding ring interposed between the joint gasket and the clamping ring. Thus, the Imhof patent requires three separate components to be assembled within the mechanical joint to produce the desired sealing and locking functions.
In some mechanical pipe joints, it is advantageous to secure pipe spigots made of various materials. For instance, in some cases, there exists a need to secure plastic pipe spigots (such as PVC piping) within a bell socket composed of a different material (such as ductile iron). In this case, however, conventional hardened steel locking segments having a relatively short length can expose the PVC pipe spigot to large localized forces that might damage the PVC material.
In addition, in mechanical piping joints having ductile iron bell sockets and glands and PVC or other plastic pipe spigots, it is advantageous to provide a lighter weight gland so that it is easier for assembly personnel to handle during pipe joint construction. In prior mechanical joints, such as those described in the Hunter '980 patent, the gland includes a “forward end” that extends axially outward from the gland. The extra material added to the gland in the “forward end” structure adds weight and manufacturing complexity to the gland structure. Thus, there exists a need for a mechanical pipe joint that utilizes a more lightweight gland that is easier to handle and is less likely to damage PVC or other plastic pipe spigots during pipe joint construction.
Thus, there exists a need in pipe industry for a mechanical pipe joint, gasket, and method for restraining a pipe spigot within a bell socket utilizing an integrated gasket that improves both: (1) sealing surface area between the inner surface of a bell socket and outer surface of a pipe spigot, and (2) restraining surface area between an inner surface of a restraining portion and an outer surface of a pipe spigot. In addition, there exists a need for locking elements that exert a restraining force that is evenly distributed around the entire circumference of the spigot outer surface, and that engage the spigot outer surface only after the sealing portion of the gasket has been compressed within the bell socket. Also, there exists a need for a mechanical pipe joint gasket that fills the bell socket with an uninterrupted sealing portion. Finally, there exists a need in the industry for a gasket that accomplishes these goals with an easy-to-assemble mechanical pipe joint, that can be utilized with piping components that are made of various materials, including PVC pipe spigots.